1. Field of the Invention
This invention relates to sound recording and reproduction by photographic means. More particularly, this invention relates to methods, articles and systems for the reproduction of sound in connection with motion pictures.
2. Description of the Prior Art
The general principle of sound recording by photographic means is old and involves exposing a photographic film to illumination controlled by the sound signals to be recorded. After the latent image thus formed on the film is developed into a projectable image, the light transmission properties of the developed film vary in sympathy with the amplitude and frequency of the sound waves. These variations in the light-transmitting properties of the film may be accomplished in a variety of ways, but it is most commonly accomplished by rendering a continually varying area of the film opaque, known as variable-area photographic recording, or by continually varying its density with respect to light transmission, known as variable-density photographic recording. In either case, the varying image produced on the film by the sound-modulated illumination is known as a "sound track," and the frequency and intensity of the variation is a function of the frequency and amplitude of the sound represented thereby.
Generally speaking, the well-known principles of sound reproduction by means of such film involve the combination of four essential elements, namely, a constant intensity light beam, some photoelectric means, means for varying the intensity of the beam predeterminately with respect to both frequency and degree, and sound reproducing means so coupled with the photoelectric means that variations of the intensity of light incident on the latter will be converted into sound. The means for varying the intensity of the light beam is provided by the above-described sound track of the film itself, which is moved continuously across the path of the beam and, as described above, thereby transmits a rapidly varying amount of the light therefrom. The output from the photocell, and therefore to the sound-reproducing means, depends on how much light falls on it and this, in turn, is controlled by the sound track on the film.
To date, processing of photographic sound recordings has been essentially similar to conventional picture materials, i.e., development of the negative image, removal of unexposed silver, from the negative exposure by a separate light source to print a positive from the negative and subsequent development and processing of the positive to bleach out the exposed silver. This procedure is time-consuming and complicated especially when the use of various dyes are involved for color film processing.
The control of temperature and composition of the developing solution have a great influence on the constancy of sound track development. Furthermore, inefficient agitation can produce distortion due to local accumulation of by-products in the region separating the clear and dense areas. When prints are made, care must be taken to obtain the proper exposure of the positive through the negative, not only as to time and intensity of light but, in the more common variable-area recording, also in terms of geometric shape of the image. Also, the shrinkage of the negative (which is not constant) must be considered. Shrinkage can vary between 0 and 1% and the slip of the negative over the unexposed positive can result in more or less pronounced distortions in sound reproduction. The effect of this shrinkage usually has been overcome by using non-slip printers in which the films only touch each other at the exposure point.
The photographic method of sound recording and reproduction has found its widest use in providing sound tracks for cinematographic film, and by far the most common technique for this application is the variable area method of recording. The cinematographic sound track is normally made on a separate negative film and then printed or "striped" alongside the picture images in what is called a "married print". The continual movement necessary for the reproduction process described hereinbefore is accomplished by the film movement through the projector.
In the production of color motion pictures, some difficulty has been encountered in producing satisfactory photographic sound tracks. Methods in the prior art generally involve processing or otherwise treating the photographic sound track portion of the motion picture film separately from the picture area, thus resulting in various complex and time-consuming procedures which decrease the desirability of photographic sound track systems over alternative methods, notably magnetic tape systems. For a further discussion concerning the development of sound recordings, see: Glafkides, P.; Photographic Chemisty; Foundation Press; London (1958) pps. 261-265.
For the above cited reasons, it would be highly desirable if the time advantages and simplicity associated with silver diffusion transfer processing could be employed in the processing of photographic sound recordings and cinematographic sound films.
Several integral silver diffusion transfer film units, essentially comprising a fixed laminate which includes a support carrying on one surface thereof a layer containing photosensitive silver halide crystals and a layer containing silver precipitating nuclei, are disclosed and claimed in several U.S. patents, including the following:
______________________________________ U.S. Pat. No. Issue Date ______________________________________ 2,861,885 11/25/58 3,536,488 10/27/70 3,615,426 10/26/71 3,615,427 10/26/71 3,615,428 10/26/71 3,615,429 10/26/71 3,677,753 7/18/72 3,894,871 7/15/75 ______________________________________
The above indicated film units are particularly suited for employment as a cinematographic film for motion picture projection, since a positive image is provided in black and white, and, where the film units also include optical screen elements, in color, with simple and effective processing employing relatively simple and stable processing compositions immediately subsequent to exposure. Such a film unit is suitably employed in a motion picture system such as that described in U.S. Pat. No. 3,615,127, issued Oct. 26, 1971 which comprises a compact motion picture cassette capable of performing the functions of exposing a photosensitive film contained therein and subsequently processing the film by applying thereon a developing composition to develop the recorded images and also projecting the images or otherwise presenting them for viewing purposes.